Heretofore, there have been proposed various tires as a safety tire capable of continuously and safely running to a place provided with equipment for exchanging or repairing the tire even if the internal tire pressure drops or disappears due to the puncture of the tire, damage of an air valve or the like.
Among them, International Publication brochure WO98/23457 and International Publication brochure WO99/32308 disclose, for example, safety tires each consisting of a combination of a tire comprising a tread portion, a pair of sidewall portions and bead portions with a toric air member placed in the tire and inflated under an internal pressure and expansion-deformed by the drop of the internal tire pressure to subrogate a load support from the tire.
In the former safety tire, two cross cord layers similar to a belt of the tire are arranged on an outer circumferential portion of the toric air member as a reinforcing member for restraint, and a pressure higher by 50–500 kPa than the internal pressure of the tire is filled into the toric air member placed in the tire in use, and if the puncture of the tire is caused, the cords of the reinforcing member for restraint are broken by an expansion force of the toric air member and hence the load support is subrogated by the expanded toric air member from the tire. The latter is a safety tire of a double tire system formed by assembling an outer tire and a torus film (toric air member) placed therein and being similar to a radial tire structure onto a rim, wherein the toric air member provided with a turnup reinforcing ply is provided on its outer circumferential portion with plural reinforcing annular elements (cords) arranged at given intervals in a widthwise direction, and if the tire is punctured, cords of the turnup reinforcing ply and the reinforcing annular elements are broken by an expansion force of the toric air member and hence the toric air member subrogates the load support from the tire.
Among these safety tires, the type of breaking the cords in the inside of the toric air member has a fear that the toric air member itself is damaged and broken by the broken cord end to loss a function as a safety tire, while the type of breaking the cords at the outside of the toric air member becomes high in the fear that the broken cords damage an outer face portion of the toric air member and an inner face portion of the tire including a carcass. In any types, therefore, it is difficult to sufficiently ensure a safe runnable distance after the puncture of the tire required in this type of the safety tire.
On the other hand, International Publication brochure WO00/30877 discloses a safety tire wherein the turnup reinforcing ply arranged in the toric air member is made of cords each consisting of a core wire and winding wires helically wound around the core wire, and the cord is durable to a pressure difference in usual running and a centrifugal force and has a structure that the core wire is broken but the winding wires are extended without breaking in the occurrence of air loss due to the puncture and the like, and a periphery sufficient to an expansion-deformation of the toric air member is given to the winding wire, whereby the occurrence of the aforementioned problem when the cords are broken as a whole can be avoided.
In this safety tire, however, it is not guaranteed that the core wire in the cord as a tension-resistant member is timely broken over a full circumference and a full width of the toric air member in the expansion-deformation of the toric air member. Up to a time that the winding wires of the cord support the expansion force of the toric air member after the breakage of the core wire in the cord, the toric air member is violently expansion-deformed under an action of a small tensile force or a small tensile stress, so that there is a problem that the toric air member is equally contacted with the full inner face of the tire.
The invention is to solve the above problems of the conventional technique and to provide a toric air bag for a safety tire capable of sufficiently and equally contacting with a full inner face of a tire without causing problems in the durability and the like resulted from the breakage of the cord itself when the toric air bag is expansion-deformed accompanied with the drop of an internal tire pressure or the like.